Descriptions, figures, distribution maps and extensive collection records of the 4 American spp. of Oropsylla are given, and their relationship to Asiatic spp. noted. All are parasites of fossorial sciurid rodents as follows: O. arctomys occurs on Marmota, especially M. monax; O. rupestris on Citellus r. richardsoni; O. alaskensis on C. parryii; and O. idahoensis on Citellus spp., especially C. (Callospermophilus) lateralis. O. arctomys (Baker) 1904 (= Aetheopsylla septentrionalis Stewart and Holland 1940, synonym).